This invention relates to an electrical connective traversal oriented in the wall of a cathode ray tube envelope and more particularly to structural means integral with the connective traversal to effect increased areal contact with internal coating in the tube and to provide regional radiation shielding of the traversal area of the envelope.
In cathode ray tubes, especially those utilized in color television applications, there has been a trend to increase the operating anode potentials. For example, in the larger sizes of display tubes it is common practice to utilize anode voltages in excess of 20 KV. With the increase in anode voltage there is also a resultant increase in x-radiation emission, such being generated by the high velocity electrons striking metallic objects within the tube such as the shadow mask and/or the aluminum film disposed in the viewing panel region of the tube. The x-rays so generated are randomly radiated in diverse directions such as towards the viewing panel and back into the funnel region of the envelope. The glass of the viewing panel is formulated to contain specific additive elements, such as lead and/or strontium, to attenuate the transmission of x-rays therethrough. The glass composition of the funnel portion of the envelope also contains additive elements for attenuating the transmission of x-rays. Furthermore, the glass comprising the funnel and viewing panel portions is of a sufficient thickness and mass to achieve a satisfactory balance for both tube strength and x-ray attenuation. However, the glass surrounding the electrical connective traversal oriented in the wall of the envelope, such as the anode connector button, is reduced in thickness resultant of the procedure for sealing of the metallic connector to the glass. Thus, the seal area of this connective traversal exhibits less x-ray attenuation than the adjacent areas of the picture tube envelope. In addition, there is a tendency for the traversal button per se to permit the transmission of problematic x-radiation therethrough. Therefore, to remedy this undesirable radiation situation, television receiver manufacturers have found it necessary to use an external connective means which is provided with a terminal shielding cap or cover made of a material to attenuate x-ray radiation emanating from this area of the tube envelope.
The electrical traversal, such as the high voltage second anode button, is a hollow member comprised of a substantially frusto-conical body, the bottom surface of which is oriented within the interior of the envelope. In the completed tube, the internal surface of the funnel portion of the envelope is provided with an essential electrical conductive coating, such as Aquadag, which intentionally makes contact with the bottom surface of the button member. The high voltage anode potential required for tube operation is applied to this interior coating from a source external of the tube by means of a terminal connection externally attached to the traversal button. The nature of the hermetic seal between the wall of the traversal button and the contiguous glass of the funnel portion is conducive to the formation of re-entrant angles therebetween, whereat coating difficulties are sometimes encountered. When deep re-entrants are formed at this seal region, poor coating adherence is an inherent resultant; a condition which produces inadequate electrical conduction between the connective button and the interior conductive coating. In addition, under higher anode voltage operation, any borderline condition, relative to the adequacy of electrical contact between the button and the coating, is more susceptible to breakdown, thereby creating an inferior connection and a potentially deleterious arcing situation within the tube.